WO2023109896A1 - 一种改进的vde-ter系统载波频偏同步方法 - Google Patents
一种改进的vde-ter系统载波频偏同步方法 Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/0014—Carrier regulation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L7/00—Arrangements for synchronising receiver with transmitter
- H04L7/02—Speed or phase control by the received code signals, the signals containing no special synchronisation information
- H04L7/033—Speed or phase control by the received code signals, the signals containing no special synchronisation information using the transitions of the received signal to control the phase of the synchronising-signal-generating means, e.g. using a phase-locked loop
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/0014—Carrier regulation
- H04L2027/0024—Carrier regulation at the receiver end
- H04L2027/0026—Correction of carrier offset
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- the invention relates to the technical field of maritime wireless communication, in particular to an improved VDE-TER system carrier frequency offset synchronization method.
- VDES VHF Data Exchange System
- AIS Automatic Identification System, Automatic Identification System
- VDES includes AIS, ASM (Application Specific Messages) and VDE (VHF Data Exchange) three business channels
- VDE includes VDE-TER (VDE-Terrestrial) and VDE-SAT (VDE-Satellite) two systems.
- VDE-TER channel provides data communication at a higher rate, therefore, there is a higher requirement for communication synchronization performance between VDE-TER transceivers.
- Carrier synchronization is to restore the received wireless signal to the state closest to the waveform of the transmitted wireless signal, so as to improve the accuracy of signal demodulation and ensure the correct transmission of information.
- carrier frequency offset synchronization is a key link in system synchronization, which directly affects the synchronization performance of VDE-TER system and whether the system can work normally.
- DA data-aided
- NDA non-data-aided
- the DA method needs to send a training sequence or pilot sequence at the sending end, and the sequence is known at the receiving end by default, and the receiving end uses this sequence for synchronization; the NDA method does not need any known sequence information, and directly uses the received data for estimation. It belongs to the blind estimation method. Since the DA method utilizes the known sequence for synchronization estimation, the range and accuracy of its frequency offset estimation are generally better than the NDA estimation method.
- an improved VDE-TER system carrier frequency offset synchronization method is provided, compared with the existing method The bit error rate of the system is reduced, and the synchronization performance of the system is improved.
- An improved VDE-TER system carrier frequency offset synchronization method runs in the VDE-TER baseband chip, and the VDE-TER baseband chip includes an analog-to-digital conversion module, a modulation and demodulation module, a pulse shaping and a matched filtering module , a frequency offset synchronization module, a phase tracking module; when the VDE-TER baseband chip is running, the data is carried out carrier synchronization based on the frequency offset synchronization module and the phase tracking module, and then data demodulation is performed based on the demodulation module;
- the method comprises the steps of:
- Carrier frequency offset estimation is performed based on the training sequence to obtain an estimated frequency offset value
- the carrier frequency offset estimation is performed based on the training sequence, and the frequency offset estimation value is obtained, including:
- the 13 frequency offset estimation values are averaged to obtain the final frequency offset estimation value.
- phase tracking is performed on the first-level compensation data segment, and the accumulated phase compensation value is obtained, so as to obtain the second-level compensation data segment, including:
- Phase offset correction is performed on each bit of data in the first-level compensation data segment based on the phase-offset compensation value of each bit, so as to obtain the second-level compensation data segment.
- the present invention has the following advantages:
- the present invention mainly aims at the frequency offset synchronization problem of the VDE-TER system, and designs a carrier frequency offset synchronization method. Based on the unique fixed training sequence of the VDE-TER system, the 13-bit Barker code and its corresponding inverse code are extracted Compensation data results make up for the lack of synchronization methods in the VDE-TER system.
- the present invention improves and adds a tracking method to obtain phase offset compensation based on the phase difference of the constellation diagram. In the case of lower frequency offset Under this condition, the bit error rate is reduced and the synchronization performance of the system is optimized.
- FIG. 1 is a flowchart of a carrier frequency offset synchronization method of the present invention.
- Fig. 2 is a block diagram of the VDE-TER baseband chip of the present invention.
- Fig. 3 is a specific execution flow of the carrier frequency offset synchronization method in the embodiment.
- Fig. 4 is a specific execution flow of phase tracking in the embodiment.
- VDE-TER baseband chip mainly comprises analog-to-digital conversion module, Modulation and demodulation module, pulse shaping and matched filter module, frequency offset synchronization module, phase tracking module; when the VDE-TER baseband chip is running, the data is synchronized based on the frequency offset synchronization module and phase tracking module, and then based on the demodulation module Perform data demodulation;
- the above method mainly includes the following steps:
- Matching filtering is performed on the data at the receiving end of the system, and a training sequence is extracted from the data segment after the matching filtering.
- the information data is modulated and pulse-shaped, it enters the receiving end through the channel.
- the modulation method uses the 16QAM specified in the protocol ITU-RM.1139-Ed.2-The-Technical-Specification-of-VDES modulation.
- the receiver performs matched filtering on the data. Both root-raised cosine filters are used for pulse shaping at the sending end of the system and matched filtering at the receiving end to eliminate intersymbol crosstalk.
- the roll-off factor specified in the VDES protocol is 0.3.
- each phase difference corresponds to obtain an estimated value of frequency offset
- this step is performed according to the following model:
- Frequency_Offset p(X Receiving_Training , T Symbol_Cycle );
- F Frequency_Offset is the estimated carrier frequency offset value
- X Receiving_Training is the extracted training sequence
- T Symbol_Cycle symbol period is the frequency offset estimated value according to the following formula:
- r(k) is a 13-bit Barker code
- r * (k+13) is the conjugate of its corresponding inverse code
- k is the number of bits
- 2 ⁇ k ⁇ 14 is the symbol period
- T is the symbol period
- f d is the estimated value of the frequency offset.
- this step will be performed according to the following model:
- F Data_Segment q(X Data , X Standard_Constellation );
- the returned F Data_Segment is the data segment after phase tracking, that is, the second-level compensation data segment
- X Data is the first-level compensation data segment obtained in step 3
- X Standard_Constellation is the standard constellation diagram of 16QAM.
- the phase tracking process in the embodiment of the present invention is shown in FIG. 4 .
- the receiving end of the system extracts the training sequence, and obtains the phase difference between the 13-bit Barker code symbol and the conjugate of the inverse code symbol corresponding thereto, and a frequency offset estimation value can be deduced from each bit of the phase difference, for 13
- the frequency offset estimation values are averaged to obtain the final frequency offset estimation value; use the frequency offset estimation value obtained in the previous step to perform frequency offset compensation on the data segment, the flow chart of this part is shown in Figure 3; since the compensated data still has Residual frequency offset, and the residual frequency offset will cause the constellation diagram to shift, so continue to perform phase tracking on each bit of data, compare the difference between the constellation diagram of a bit of data after rough synchronization and the accurate constellation diagram, and add the previous data The phase difference obtained by bit-by-bit comparison of the constellation diagram is used as the phase offset compensation value of the next bit.
- phase difference of the constellation diagram is compared again, and the previous phase difference is continued to be accumulated, and so on.
- the flow chart of this part is shown in Figure 4 Shown; After phase tracking, the final data segment after carrier frequency offset synchronization is obtained.
- the sending end sends a frame of data, adding an original frequency offset value of 150 Hz, and the channel is an AWGN channel.
- Receiving_Training Receiving_Training_Sequence
- Estimated_Frequency_Offset 151.4996Hz
- Receiving_Training_Sequence is the training sequence extracted by the receiving end
- Estimated_Frequency_Offset is the estimated value of frequency offset
- Standard_Constellation Standard_Constellation_Chart
- Data_Segment is the data segment compensated by the estimated frequency offset value
- Standard_Constellation_Chart is the standard constellation diagram of 16QAM specified in the VDES protocol
- Tracking_Valid_Data_Segment is the data segment after phase tracking.
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Abstract
本发明提供一种改进的VDE-TER系统载波频偏同步方法，包括：在系统接收端对数据进行匹配滤波，由匹配滤波后的信息数据段提取训练序列；基于所述训练序列进行载波频偏估计，获取频偏估计值；基于所述频偏估计值对所述信息数据段进行频偏补偿，从而获得一级补偿数据段；对所述一级补偿数据段进行相位跟踪，获取累积相位补偿值，从而获得二级补偿数据段；对所述二级补偿数据段进行解调，获取同步后的接收信息。本发明采用改进的基于双巴克码训练序列的载波频偏同步方法进行频偏同步，并增加了跟踪方法，在较低频率偏移的情况下，降低了误码率，优化了系统的同步性能。
Description
本发明涉及海上无线通信技术领域，具体而言，尤其涉及一种改进的VDE-TER系统载波频偏同步方法。
海上甚高频数据交换系统(VHF Data Exchange System,VDES)是针对AIS(Automatic Identification System,自动识别系统)的加强和升级的系统。VDES包含AIS、ASM(Application Specific Messages)和VDE(VHF Data Exchange)三种业务信道，VDE又包括VDE-TER(VDE-Terrestrial)和VDE-SAT(VDE-Satellite)两大系统。相比AIS，VDE-TER信道提供了更高速率的数据通信，因此，VDE-TER收发机之间就有更高的通信同步性能的要求。载波同步是为了将接收到的无线信号恢复到最接近发送的无线信号波形状态，以提高信号解调正确率，保证信息的正确传输。在无线数字通信中，由于收发机晶振电路不稳定，信号会引入频率偏移，从而导致信号无法正确判决，系统误码率增大，同步性能下降。因此，载波频偏同步是系统同步中的关键一环，直接影响到VDE-TER系统的同步性能以及系统是否能够正常工作。
目前现有的频偏同步方法主要分为两种类型，数据辅助(DA,Data-Aided)方法和非数据辅助(NDA,Non-Data-Aided)方法。DA方法需要在发送端发送训练序列或导频序列，并在接收端默认该序列已知，接收端利用该序列进行同步；NDA方法不需要任何已知的序列信息，直接利用接收数据进行估计，属于盲估计方法。由于DA方法利用了已知序列进行同步估计，所以其频偏估计的范围和精度一般要优于NDA估计方法。
但目前针对于VDE-TER系统的载波频偏同步方法较少。对于现有的两类传统频偏同步方法DA和NDA来说，由于VDE-TER中每帧数据都含有固定已知的训练序列，并且训练序列由1位1和13位巴克码和13位巴克码反码组成，故该系统更加适用DA同步方法，并且DA方法精度更高。但将现 有的DA方法直接应用于VDE-TER系统中时，误码率较高，系统无法正常工作，因此传统DA方法对于VDE-TER系统的适用性较低。
发明内容
根据上述提出现有频偏同步方法误码率较高且与VDE-TER系统的适应性低的技术问题，而提供一种改进的VDE-TER系统载波频偏同步方法，与现有方法相比降低了系统误码率，提升了系统同步性能。
本发明采用的技术手段如下：
一种改进的VDE-TER系统载波频偏同步方法，所述方法运行在VDE-TER基带芯片中，所述VDE-TER基带芯片包括模数转换模块、调制解调模块、脉冲成型与匹配滤波模块、频偏同步模块、相位跟踪模块；所述VDE-TER基带芯片运行时，基于频偏同步模块和相位跟踪模块对数据进行载波同步，然后基于解调模块进行数据解调；
所述方法包括以下步骤：
在系统接收端对数据进行匹配滤波，由匹配滤波后的信息数据段提取训练序列；
基于所述训练序列进行载波频偏估计，获取频偏估计值；
基于所述频偏估计值对所述信息数据段进行频偏补偿，从而获得一级补偿数据段；
对所述一级补偿数据段进行相位跟踪，获取累积相位补偿值，从而获得二级补偿数据段；
对所述二级补偿数据段进行解调，获取同步后的接收信息。
进一步地，基于所述训练序列进行载波频偏估计，获取频偏估计值，包括：
获取训练序列中13位巴克码和与其对应的13位巴克码的反码；
求取训练序列中13位巴克码反码的共轭；
将13位巴克码反码的共轭与13位巴克码一一对应，并分别求取相差，每个相差对应可求得一个频偏估计值；
对13个频偏估计值取平均得到最终的频偏估计值。
进一步地，对所述一级补偿数据段进行相位跟踪，获取累积相位补偿值，从而获得二级补偿数据段，包括：
获取一级补偿数据段中每一位数据的星座图与准确星座图之间的相差；
累加上前面数据位比较星座图得到的相差，作为下一位的相偏补偿值；
基于每一位的相偏补偿值对一级补偿数据段中的每一位数据进行相偏纠正，从而获得二级补偿数据段。较现有技术相比，本发明具有以下优点：
1、本发明主要针对VDE-TER系统的频偏同步问题，设计了一种载波频偏同步方法，基于VDE-TER系统特有的固定训练序列，提取的是13位巴克码与其对应的反码获取补偿数据结果，弥补了VDE-TER系统缺乏同步方法的空白。
2、本发明在现有的基于双巴克码训练序列的载波频偏同步方法基础上，进行了改进，并增加了跟踪方法，基于星座图相差获取相偏补偿，在较低频率偏移的情况下，降低了误码率，优化了系统的同步性能。
为了更清楚地说明本发明实施例或现有技术中的技术方案，下面将对实施例或现有技术描述中所需要使用的附图做以简单地介绍，显而易见地，下面描述中的附图是本发明的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动性的前提下，还可以根据这些附图获得其他的附图。
图1为本发明载波频偏同步方法流程图。
图2为本发明VDE-TER基带芯片模块图。
图3为实施例中载波频偏同步方法具体执行流程。
图4为实施例中相位跟踪具体执行流程。
为了使本技术领域的人员更好地理解本发明方案，下面将结合本发明实 施例中的附图，对本发明实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例仅仅是本发明一部分的实施例，而不是全部的实施例。基于本发明中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都应当属于本发明保护的范围。
另外，目前针对VDE-TER系统的频偏同步，有一种方法利用该系统训练序列为双巴克码的特殊结构进行频偏同步。该方法误码率虽然低于DA方法，但该方法适用于频偏较大的情况，当频偏较小时，系统误码率会升高，其同步性能下降。本发明即在该方法的基础上进行了改进和添加。
如图1所示，一种改进的VDE-TER系统载波频偏同步方法，所述方法运行在VDE-TER基带芯片中，如图2所示，VDE-TER基带芯片主要包括模数转换模块、调制解调模块、脉冲成型与匹配滤波模块、频偏同步模块、相位跟踪模块；当VDE-TER基带芯片运行时，基于频偏同步模块和相位跟踪模块对数据进行载波同步，然后基于解调模块进行数据解调；
上述方法主要包括以下步骤：
S1、在系统接收端对数据进行匹配滤波，由匹配滤波后的数据段提取训练序列。
具体来说，在发送端，信息数据经过调制、脉冲成型后，经过信道进入接收端，调制方式使用协议ITU-RM.1139-Ed.2-The-Technical-Specification-of-VDES中规定的16QAM调制。然后接收端对数据进行匹配滤波。在系统发送端对脉冲成型与在接收端匹配滤波均使用根升余弦滤波器，消除码间串扰，其中VDES协议中规定滚降因子为0.3。
S2、基于所述训练序列进行载波频偏估计，获取频偏估计值。具体来说，包括：
S201、获取训练序列中13位巴克码和与其对应的13位巴克码的反码；
S202、求取训练序列中13位巴克码反码的共轭；
S203、将13位巴克码反码的共轭与13位巴克码一一对应，并分别求取相差，每个相差对应可求得一个频偏估计值；
S204、对13个频偏估计值取平均得到最终的频偏估计值。
具体来说，该步骤按照下述模型进行执行：
F
Frequency_Offset＝p(X
Receiving_Training,T
Symbol_Cycle)；
式中，F
Frequency_Offset为估计的载波频偏值，X
Receiving_Training为提取到的训练序列，T
Symbol_Cycle符号周期。优选地，本发明根据以下公式计算获取频偏估计值：
其中r(k)为13位巴克码，r
*(k+13)为与其对应的反码的共轭，k为位数，2≤k≤14,T为符号周期，
为相差，f
d为频偏估计值。
S3、基于所述频偏估计值对所述信息数据段进行频偏补偿，从而获得一级补偿数据段。
S4、对所述一级补偿数据段进行相位跟踪，获取累积相位补偿值，从而获得二级补偿数据段。具体包括：
S401、获取一级补偿数据段中每一位数据的星座图与准确星座图之间的相差；
S402、累加上前面数据位比较星座图得到的相差，作为下一位的相偏补偿值；
S403、基于每一位的相偏补偿值对一级补偿数据段中的每一位数据进行相偏纠正，从而获得二级补偿数据段。
具体来说，该步骤将按照下述模型进行执行：
F
Data_Segment＝q(X
Data,X
Standard_Constellation)；
式中，模型执行完毕后，返回F
Data_Segment为相位跟踪后的数据段，即二级补偿数据段，X
Data为步骤3得到的一级补偿数据段，X
Standard_Constellation为16QAM的标准星座图。优选地，本发明实施例中的相位跟踪过程如图4所示。
S5、对所述二级补偿数据段进行解调，获取同步后的接收信息。
下面通过具体的应用实例对本发明的方案做进一步说明。
本实施例中，系统接收端提取训练序列，求得其中13位巴克码符号和与其对应的反码符号的共轭的相差，每一位的相差都可推导出一个频偏估计值，对13个频偏估计值取平均得最终的频偏估计值；使用上一步得到的频偏估计值对数据段进行频偏补偿，此部分的流程图如图3所示；由于补偿后的数据仍有残留频偏，而残留频偏会导致星座图偏移，因此继续对每一位数据进行相位跟踪，比较粗同步后的一位数据的星座图与准确星座图之间的相差，累加上前面数据位比较星座图得到的相差，作为下一位的相偏补偿值，下一位相偏纠正后，再比较星座图的相差，继续累加之前的相差，以此类推，此部分的流程图如图4所示；相位跟踪后得到最终的载波频偏同步后的数据段。
具体来说，本实施例中，发送端发送一帧数据，加入原始频率偏移值为150Hz，信道为AWGN信道。
(1)载波频偏粗估计结果
输入：
X
Receiving_Training＝Receiving_Training_Sequence；
T
Symbol_Cycle＝1/76800；
输出：
Estimated_Frequency_Offset＝151.4996Hz；
Receiving_Training_Sequence为接收端提取到的训练序列，Estimated_Frequency_Offset为频偏估计值。
(2)相位跟踪结果
输入：
X
Data＝Data_Segment；
X
Standard_Constellation＝Standard_Constellation_Chart；
输出：
Data＝Tracking_Valid_Data_Segment；
说明：Data_Segment为使用频偏估计值补偿后的数据段，Standard_Constellation_Chart为VDES协议中规定的16QAM的标准星座图，Tracking_Valid_Data_Segment为相位跟踪后的数据段。
(3)最终系统误码率结果
本发明方法的误码率err＝0。
(4)原始方法估计结果
原始方法的频偏估计值为205.7408Hz，系统误码率err＝0.3973。
最后应说明的是：以上各实施例仅用以说明本发明的技术方案，而非对其限制；尽管参照前述各实施例对本发明进行了详细的说明，本领域的普通技术人员应当理解：其依然可以对前述各实施例所记载的技术方案进行修改，或者对其中部分或者全部技术特征进行等同替换；而这些修改或者替换，并不使相应技术方案的本质脱离本发明各实施例技术方案的范围。
Claims (3)
- 一种改进的VDE-TER系统载波频偏同步方法，其特征在于，所述方法运行在VDE-TER基带芯片中，所述VDE-TER基带芯片包括模数转换模块、调制解调模块、脉冲成型与匹配滤波模块、频偏同步模块、相位跟踪模块；所述VDE-TER基带芯片运行时，基于频偏同步模块和相位跟踪模块对数据进行载波同步，然后基于解调模块进行数据解调；所述方法包括以下步骤：在系统接收端对数据进行匹配滤波，由匹配滤波后的信息数据段提取训练序列；基于所述训练序列进行载波频偏估计，获取频偏估计值；基于所述频偏估计值对所述信息数据段进行频偏补偿，从而获得一级补偿数据段；对所述一级补偿数据段进行相位跟踪，获取累积相位补偿值，从而获得二级补偿数据段；对所述二级补偿数据段进行解调，获取同步后的接收信息。
- 根据权利要求1所述的一种改进的VDE-TER系统载波频偏同步方法，其特征在于，基于所述训练序列进行载波频偏估计，获取频偏估计值，包括：获取训练序列中13位巴克码和与其对应的13位巴克码的反码；求取训练序列中13位巴克码反码的共轭；将13位巴克码反码的共轭与13位巴克码一一对应，并分别求取相差，每个相差对应可求得一个频偏估计值；对13个频偏估计值取平均得到最终的频偏估计值。
- 根据权利要求2所述的一种改进的VDE-TER系统载波频偏同步方法，其特征在于，对所述一级补偿数据段进行相位跟踪，获取累积相位补偿值，从而获得二级补偿数据段，包括：获取一级补偿数据段中每一位数据的星座图与准确星座图之间的相差；累加上前面数据位比较星座图得到的相差，作为下一位的相偏补偿值；基于每一位的相偏补偿值对一级补偿数据段中的每一位数据进行相偏纠 正，从而获得二级补偿数据段。
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